How can you restrict date selection with a 3 week period?

Basically, when making a booking we require 3 weeks notice. I would like to be able to restrict users from booking less than our required term using the calendar widget. 

We have a date reservation widget: https://widgets.jotform.com/widget/date_reservation, unfortunately, it does not have the option to disable dates in a custom range.

You might want to use a regular date field which allows you to disable dates, however, it does not have a reservation functionality: https://www.jotform.com/help/337-How-to-Use-the-Date-Limits-Option 

Let us know if you have more questions.